Letters 99.28

Metrodorus says: ‘There is a certain pleasure which is related to sadness.’ We Stoics may say that, but you may not. The only Good which you recognize, is pleasure, and the only Evil, pain; and what relationship can there be between a Good and an Evil? But suppose that such a relationship does exist; now, of all times, is it to be rooted out? Shall we examine grief also, and see with what elements of delight and pleasure it is surrounded?

Seneca, Letters to Lucilius 99.28, translated by Richard Mott Gummere